Transcript TROPISMS
Plant Movements Tropisms and Turgor Responses 1 2 Tropisms The growth of part of a plant towards or away from an environmental stimulus. If the growth is towards the stimulus, the tropism is said to be positive, if it is away from the stimulus it is said to be negative. Tropisms are a directional response – the environmental stimulus comes from one direction. 3 Types of Tropisms The type of the stimulus is shown by prefixes: Photo Light Geo Gravity or Gravi Hydro Chemo Thigmo Water Chemicals Touch 4 Plant Physiology Video http://www.youtub e.com/watch?v=z ctM_TWg5Ik&featur e=fvw This video shows how Tropisms work 5 Examples of Tropisms The shoot of a plant is positively phototropic - it grows towards light. 6 Examples of Tropisms Roots of plants are positively geotropic – they grow down, and shoots are negatively geotropic – they grow up 7 More Examples of Tropisms Some roots grow away from copper pipes – they are negatively chemotropic Plants such as runner beans are positively thigmotropic – they grow towards a supporting structure such as another plant. 8 Turgor Responses These are responses of plants to stimuli from the environment that do not come from a particular direction. These include responses to changes in temperature, light intensity, humidity and touch. 9 Videos of Mimosa Plant and Venus Fly Trap http://www.youtube.com/watch?v=BLTc VNyOhUc http://www.youtube.com/watch?v=PRo4r g07_gg&feature=fvw 10 Examples of Turgor Responses •The leaves of the Venus Fly Trap and the Mimosa plants both close up in response to touch. The closure is not in one particular direction. •The flowers and leaves of many plants close up when the light intensity decreases (it gets dark), regardless of where light is or isn’t. 11 Differences between Tropisms and Turgor Responses: Tropisms are a directional response, the stimulus (eg. sunlight through a window) determines the direction the plant grows. Turgor Responses are not the result of a stimulus from a certain direction. Turgor Responses can be fast and do not result from cell growth, whereas Tropisms are generally slow growth changes.